Listeria monocytogenes is facultative intracellular food-borne pathogen that provides an extremely amenable model for basic studies on host-pathogen interactions. A primary determinant of L. monocytogenes pathogenesis is Listeriolysin O (LLO), a member of a large family of pore-forming cytolysins that is largely responsible for mediating escape of L. monocytogenes from a phagosome and for virulence. LLO activity is a double-edged sword as its activity must be restricted to an acidic phagosome or the host cell will die due to LLO-mediated cell death (referred to as compartmentalization). In contrast, the ActA protein is only expressed by bacteria when they reach the host cytosol. Despite the fact that LLO and ActA act in different compartments and at different times during the infection cycle, the transcription of both is entirely dependent on the same Crp family transcription factor PrfA. PrfA is predicted to bind an activating ligand, but the nature of the ligand is not known. During the prior funding period, we developed innovative tools and performed extensive genetic screens to identify L. monocytogenes determinants that regulate compartment-specific expression of LLO and ActA. The results of the screens implicate a critical role of redox stress as a mediator of compartmentalization. L. monocytogenes mutants lacking glutathione synthase (GshF) expressed very low levels of ActA during cytosolic growth and were greater than 1000-fold less virulent in mice. These data suggest that cytosolic L. monocytogenes are experiencing redox stress, but of unknown origin. However, the defect in ActA expression was rescued by a mutation that locks PrfA in its activated state, strongly suggesting that a primary role for glutathione is to mediate PrfA activation and we hypothesize that glutathionylation is the activating ligand. We also found that LLO is glutathionylated. We hypothesize that glutathionylation protects the LLO cysteine from irreversible oxidation in a phagosome prevents its activity in the cytosol. We propose to test the role of glutathione on LLO activity and compartmentalization, evaluate the role played by glutathione in PrfA activation and test the hypothesis that PrfA is a sensor of phagosomal and cytosolic redox stress.

Public Health Relevance

Diseases caused by intracellular pathogens (for example, tuberculosis, AIDS, and malaria) remain one of the largest challenges facing the international biomedical community. The proposed studies on Listeria monocytogenes will provide insight into the molecular biology and cell biology relevant to the treatment and prevention of diseases caused by intracellular pathogens.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
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Host Interactions with Bacterial Pathogens Study Section (HIBP)
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Mills, Melody
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University of California Berkeley
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Whiteley, Aaron T; Ruhland, Brittany R; Edrozo, Mauna B et al. (2017) A Redox-Responsive Transcription Factor Is Critical for Pathogenesis and Aerobic Growth of Listeria monocytogenes. Infect Immun 85:
Portman, Jonathan L; Huang, Qiongying; Reniere, Michelle L et al. (2017) Activity of the Pore-Forming Virulence Factor Listeriolysin O Is Reversibly Inhibited by Naturally Occurring S-Glutathionylation. Infect Immun 85:
Mitchell, Gabriel; Isberg, Ralph R (2017) Innate Immunity to Intracellular Pathogens: Balancing Microbial Elimination and Inflammation. Cell Host Microbe 22:166-175
Whiteley, Aaron T; Garelis, Nicholas E; Peterson, Bret N et al. (2017) c-di-AMP modulates Listeria monocytogenes central metabolism to regulate growth, antibiotic resistance and osmoregulation. Mol Microbiol 104:212-233
Portman, Jonathan L; Dubensky, Samuel B; Peterson, Bret N et al. (2017) Activation of the Listeria monocytogenes Virulence Program by a Reducing Environment. MBio 8:
Xiong, Xiaolu; Jiao, Jun; Gregory, Anthony E et al. (2016) Identification of Coxiella burnetii CD8+ T-Cell Epitopes and Delivery by Attenuated Listeria monocytogenes as a Vaccine Vector in a C57BL/6 Mouse Model. J Infect Dis :
Burke, Thomas P; Portnoy, Daniel A (2016) SpoVG Is a Conserved RNA-Binding Protein That Regulates Listeria monocytogenes Lysozyme Resistance, Virulence, and Swarming Motility. MBio 7:e00240
Reniere, Michelle L; Whiteley, Aaron T; Portnoy, Daniel A (2016) An In Vivo Selection Identifies Listeria monocytogenes Genes Required to Sense the Intracellular Environment and Activate Virulence Factor Expression. PLoS Pathog 12:e1005741
Mitchell, Gabriel; Chen, Chen; Portnoy, Daniel A (2016) Strategies Used by Bacteria to Grow in Macrophages. Microbiol Spectr 4:
Durack, Juliana; Burke, Thomas P; Portnoy, Daniel A (2015) A prl mutation in SecY suppresses secretion and virulence defects of Listeria monocytogenes secA2 mutants. J Bacteriol 197:932-42

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